The Gaza Strip will soon become entirely dependent on foreign aid and face "disastrous consequences" if the Hamas-controlled territory remains sealed off, a senior UN official warned Thursday. Israel and Egypt closed their crossings with Gaza to all but humanitarian aid after Hamas seized power in the coastal strip in June. The closures have exacerbated poverty among the 1.4 million residents of the already impoverished territory. The blockade has created a highly volatile situation, and the window of opportunity for addressing it "is small and closing fast," said Filippo Grandi, the deputy head of UN Relief and Works Agency, the international body responsible for Palestinian refugees. "Gaza risks becoming a virtually 100 percent aid dependent, closed down and isolated community within a matter of months or weeks, if the present regime of closure continues," Grandi told reporters Thursday at a Gaza City press conference. Failure to open the crossings will "lead to disastrous consequences" and an "atmosphere of hopelessness and despair in which extremism is likely to take hold," he cautioned. The cumulative losses to industry in Gaza has reached $23 million since the Hamas takeover, according to figures released Thursday by the Association of Palestinian Businessmen. If the closure continues, at least 120,000 workers in Gaza could lose their jobs, the association said. Even before Hamas' Gaza takeover, 1.1 million Gazans received foreign food assistance, a figure that rose sharply as a result of Israeli trade restrictions and an international aid embargo imposed after Hamas won 2006 elections. Two weeks ago, the Palestinian Federation of Industries reported that the closure of Gaza had forced the dismissal of about 70,000 of 120,000 private sector workers, driving unemployment above 40 percent.